'bittern' originates from Middle English, specifically the word 'bitour', which was derived from Old French 'butor', and ultimately from Latin 'butitaurus', where 'būti-' meant 'bittern' and 'taurus' meant 'bull', referring to the bird's booming call.

'bitour' transformed into the modern English word 'bittern'.

Initially, it referred to the bird's booming call, and this meaning has largely remained the same in modern usage.